I’m going to interpret your question to be a bit broader than it sounds, because a species is a quite narrow concept and would leave us looking for which species of bird, mammal, frog, etc has 1 or 2 individuals left at this exact moment. Given the current rate of extinction there are probably dozens of species that would meet these criteria and are in their last few days or weeks right now. What is of greater interest, I think, is which general type of organism is most likely to go extinct and at this moment I would place my money on tropical frogs.

First of all, the diversity of practically all kinds of species is much higher in the tropics but at the same time there tend to be fewer individuals in each species. Our common Wood frog, for example, consists of millions of individuals spread completely around the northern hemisphere in cooler forests whereas many tropical frog species entire range may consist of only the east or west sides of a few mountains. Fewer individuals and a small range, mean that it does not take a large-scale effect to wipe them out.

Frogs also aren’t nearly as good at long distance movement as birds, mammals or even insects and so if they go extinct on one tropical mountain there is only a slight chance that they will recolonize from a similar nearby mountain. If they only occur in small numbers on a few mountains, then extinction could easily happen.

Frogs experience the world in large measure through direct contact with their skin and so changes in water availability or increases in pollutants may hit them especially hard. Since frogs also tend to have quite narrow tolerances for temperature and moisture variation, they are more vulnerable to climate change, a phenomenon that nearly everyone recognizes as occurring at an accelerating rate.

In some areas of the tropics frogs are experiencing massive diebacks, with all but a few of the most abundant and adaptable species disappearing. The immediate cause seems to be a type of fungus called a chytrid but why the chytrid fungus should spread so quickly and cause extinction in so many areas is a puzzle. The most likely causes are global warming and deforestation, forces that could decrease the health of frogs so that a disease-causing organism like a chytrid might suddenly have a greater effect. In cool tropical forests at 1000 meters elevation and up, extinction can be very rapid and involve many species. The greatest effects seem to be found in cloud forests – tropical forests usually found at 1500 meters and up. Such forests have been documented to experience significant climatic warming and drying in recent years. One theory for this increased temperatures in the tropics means that moist air carried in from the eastern side and passing over the mountains will have to rise to a higher elevation before it cools enough for clouds to form. Cloud forests are tropical forests that are wet throughout the year, with clouds wetting them even when it’s not raining. If these clouds fail to form as much, the forests may become less wet and the organisms living in them, including frogs, will not be as wet as before. Another possibility is that deforestation at lower elevations may mean less water evaporated from the trees into the winds passing over them, possibly leading to drier winds that would not form clouds until higher elevations, This could also cause a drying out of the high elevation forests. Either or both of these causes could be stressing the frogs. In one well-documented case in a Costa Rican cloud forest region, about one half of the amphibian species disappeared between 1989 and 1991!

Amphibians in general are in big trouble, with at least one third globally threatened with extinction – a much higher percentage than for mammals or birds. But in tropical regions the situation can be especially dire. In one group of brightly colored Latin American frogs, Atelopus, over 80 % have gone extinct. In the last few years’ scientists working in several area of the mountains of Panama have witnessed virtually the total extinction of all frogs species except for a handful of common, widespread ones.

Many people consider frogs to be like the canary in the mineshaft, i.e., organisms whose health tells us a lot about what is happening to our environment. They respond first to changes that may eventually affect us. Are they an early warning signal? To find out more about threats to amphibians, look at <www.globalamphibians.org>